1. Field of the Invention
The present invention relates to an organic thin film transistor and method of manufacturing the same, and more particularly, to an organic thin film transistor having a low driving voltage and a good carrier mobility and method of manufacturing the same.
2. Discussion of the Related Art
A thin film transistor (“TFT”) device used as a switching element of a liquid crystal display (“LCD”) apparatus generally includes an active layer made of amorphous silicon or polysilicon. However, an organic thin film transistor (hereinafter, referred to as “OTFT”) in which the active layer is formed using an organic semiconductor material has recently been introduced as a substitute for amorphous or polysilicon based TFTs.
In particular, the active layer of the OTFT is formed by depositing an organic semiconductor material using a spin coating method or a vacuum deposition method. Advantages of OTFTs include low temperature deposition capabilities, process flexibility, relatively easy processing, and the like.
FIG. 1 is a sectional view of a related OTFT. The related OTFT includes a transparent substrate 10, a gate electrode 11, a gate insulation film 12, a source electrode 13, a drain electrode 14, and an organic semiconductor film 15. The organic semiconductor film 15 is comprised of an organic semiconductor material having a large grain size, such as pentacene.
An OTFT formed using pentacene has good mobility characteristics having the same level as an amorphous silicon TFT and is very stable in the air. However, the OTFT having the structure shown in FIG. 1 has draw backs when being used as a switching element (or a general purpose semiconductor device) in an LCD apparatus because of a high gate-source voltage (Vgs) and low carrier mobility. In particular, pentacene, which is usually used to form the organic semiconductor film 15, is influenced significantly by the characteristics of the gate insulation film 12. As a result, the grain size of pentacene forming the organic semiconductor film 15 does not grow very large during fabrication due to the gate insulation film 12, thereby producing poor carrier mobility.
To solve this problem, Korean Patent Publication No. 2004-0067047 proposes techniques in which the organic semiconductor film is deposited using spin coating. In an organic light emitting diode (OLED), driving voltage is decreased while carrier mobility is improved because one of the multi-layer structures between two electrodes in an OLED is made of a lithium fluoride (LiF) insulation film. Therefore, such principle is applied to the OTFT in the related art by adding the LiF insulation film to the OTFT.
However, the related art device also suffers from various limitations. For instance, the thickness of the organic semiconductor film is relatively large—i.e., about 4000 Å (angstroms) or higher, due as a result of the spin coating process. Accordingly, the related art method has problems in that the tunneling effect of carriers generated is limited, and, as a result, a high driving voltage is required.